1. Field of the Invention
The invention relates to a tilt-compensating indicator device for a compass having a magnetic field detection means which is mounted on a conical pivot bearing, the magnetic field detection means being capable of rotating in an essentially horizontal plane when the conical pivot bearing is vertically orientated, which is located in a housing of the compass, comprising a bottom and a top.
2. Description of the Prior Art
A tilt-compensating indicator device of this type is known from Swiss Patent No. 683,373 which is owned by the applicant. This commercially marketed tilt-compensating indicator device, which has proved its usefulness in practice, is separately mounted from the magnetic field detector and is connected with it by means of a dog. This avoids the disadvantages which occurr in a customary mechanical compass in which the indicator device is rigidly and directly connected to, or is identical with the magnetic field detector, namely that when the compass is tilted at a relatively small angle (8.degree.-12.degree.) an indicator needle or an indicator disc in the indicator device comes into contact with the top or the bottom of the housing. This disturbing effect can also occur due to different inclinations in the magnetic field of the earth when the compass is used at different latitudes.
As a result, the compass is no longer able to function properly. Before it is read, it must therefore be brought into a position where the indicator device can once more swing freely. But in many applications, e.g., orienteering, it is extremely important that the display can be accurately read as quickly as possible, i.e. without being delayed by having to re-orient the compass. In addition, tilting of the compass can disadvantageously result in bearing errors.
The known type of tilt-compensating indicator device for a compass is capable of eliminating or at least reducing the above-mentioned undesirable effects. However, it possesses the disadvantage that the bearing of the indicator device is costly to construct, and in addition the bearing must be accurately aligned in an axial direction. The axial alignment of the bearing of the indicator device with the bearing of the magnetic field detector is labor intensive.
The compass which is described in U.S. Pat. No. 2,446,258 is designed in particular for aircraft. It possesses a compass housing in which an indicator device rotates around an axis which is fixed vertically in the housing, in a plane perpendicular to this vertical axis. A frame running parallel to the vertical axis is firmly connected to the indicator device. A magnetic needle acting as a magnetic field detector which rotates via bearing elements around a horizontal axis defined by these bearing elements is mounted in this frame. The mounting of the magnetic needle in the frame ensures that the needle remains parallel to the magnetic field of the earth.
From Swedish Patent No. 127,623 there is known a liquid-filled compass having a compass needle with two floating bodies being arranged at its underside. These two floating bodies serve for keeping the needle in a horizontal position in non-horizontal earth magnetic fields by their buoyancy. Because of this, a parallel guidance of the needle in respect to a bottom and/or a top of the housing is prevented when the housing is tilted.